Were he alive today, Bach surely would have appreciated the deeply held religious beliefs of Arvo Part (Eastern Orthodox, in the case of the Estonian-born composer) and the music that enshrines them. Part's 80th birthday season has been observed by several local choral groups, including, in recent months, the Chicago Chorale and Bella Voce, and on Saturday night at Mount Carmel Church in the city's Lakeview neighborhood, the William Ferris Chorale lent its massed voices to the Part celebration.

The centerpiece of director Paul French's program was Part's "Berliner Messe" (Berlin Mass), written for the 1990 Berlin German Catholic Days festival. The music was intended to be sung liturgically during Pentecost and adheres to the quiet and devout dignity of Part's spare, neo-medieval manner, but in a less ascetic style than his earlier works.

The six-movement version for chorus and organ accompaniment made a wondrous effect, the music's sonorities wafting from the choir loft to timeless effect in the resonant church acoustics.

The Ferris Chorale has made enormous strides under French's direction, and the present incarnation is a more versatile, more technically and musically secure, more finely disciplined choral body than ever. It proved as much in its imaginatively chosen survey of familiar and unfamiliar Gallic choral pieces by Francis Poulenc, Jean Langlais and Pierre Villette, including Poulenc's ravishing "Prayers of St. Anthony" with its intriguing chromaticism. The care with which the chorale members matched pitches in these lovely and colorful works was no less exact than in their singing of the Part mass.

The chorale has made supporting the coming generation of choral singers part of its mission, and in several brief American pieces it was gratifying to hear French's group performing shoulder to shoulder with the young Spirito! Bravura chorus, which is made up of 76 female high school students under the direction of Molly Lindberg. Whether singing on their own or with the Ferris contingent, they made a splendid showing.